FIG. 20 is a cross-sectional view showing a liquid crystal display (LCD) apparatus disclosed in JP-A-2004-279262. The LCD apparatus includes a liquid crystal display member J1, an optical member J2 (e.g., an optical sheet and a diffusion sheet) disposed behind the liquid crystal display member J1, a light-emitting diode (LED) J3 as a light source element, a circuit board J4 having a LED drive circuit, a LED control circuit and a liquid crystal drive circuit, a light guide plate J5 as a light waveguide path for guiding light emitted by the LED 3, a reflector plate J6 for directing light to the front surface of the light guide plate J5.
The LED drive circuit has a switching element for switching the LED J3 on and off. The LED control circuit is for controlling timing of the switching on and off of the LED J3. The liquid crystal drive circuit is for driving the liquid crystal display member J1.
In the LCD apparatus, the LED J3 emits light at the timing controlled by the LED control circuit. The emitted light is introduced into the light guide plate J5 through the end surface. The introduced light is directed to the front surface of the light guide plate J5 by the reflector plate J6 disposed behind the light guide plate J5. Thus, the directed light is applied to the back surface of the liquid crystal display member J1 disposed in the front of the light guide plate J5. Therefore, when the liquid crystal drive circuit drives the liquid crystal display member J1, a display appears on the liquid crystal display member J1.
When the display is performed on the liquid crystal display member J1, the LED drive circuit for driving the LED J3 generates heat. For example, the switching element of the LED drive circuit generates heat. If the generated heat is transferred to components deposed near the LED drive circuit, the heat may affect the components. For example, if the heat is transferred to the light guide plate J5 made of acrylic susceptible to heat, the light guide plate J5 may be deformed. If the heat affects a complicated circuit such as the liquid crystal drive circuit for driving the liquid crystal display member J1, a wrong display may appear on the liquid crystal display member J1.
In order to prevent the problem, the circuit board J4 having the LED drive circuit is connected with a metal heat release plate extending to the back of the LCD apparatus far away from the circuit board J4. The heat release plate serves as a cooling module and releases the heat at the back of the LCD apparatus.
However, the heat release plate has high heat resistance, because the heat release plate is directly jointed to the circuit board J4. Further, the heat release plate is connected to the circuit board J4 in a wide area so that the heat tends to spread widely around the LED drive circuit. Therefore, a large portion of the heat generated by the LED drive circuit is released near the LED drive circuit and affects the components disposed near the LED drive circuit.
In the display apparatus, although the heat release plate extends to the back of the display apparatus, the heat release plate cannot fully transport the heat to the back of the display apparatus due to the high heat resistance and the wide shape. Therefore, a large portion of the heat generated by the LED drive circuit is released near the LED drive circuit. Consequently, the components disposed near the LED drive circuit may be subjected to high temperature.